A practical transmitter device for passive state BB84 quantum key distribution

TL;DR

This paper presents a simplified, passive quantum key distribution transmitter that combines state preparation and QRNG, demonstrated over 10 km fiber with a practical secret key rate, enhancing security and reducing complexity.

Contribution

A novel passive QKD transmitter design that integrates state preparation and QRNG, simplifying implementation and improving security against side-channel attacks.

Findings

Successfully established a 10 km fiber QKD link

Achieved a secret key rate of 110 bits/sec

Demonstrated practical deployment potential in urban networks

Abstract

In prepare-and-measure quantum key distribution systems, careful preparation of quantum states within the transmitter device is a significant driver of both complexity and cost. Moreover, the security guarantees of such systems rest on the correct operation of high speed quantum random number generators (QRNGs) and the high-fidelity modulation of weak optical signals by high-speed optoelectronic devices, all of which must be hardened against a variety of known side-channel attacks. A fully passive state preparation approach elegantly resolves these problems by combining state preparation and QRNG stages into a single optical instrument. By using pairs of optical pulses from a gain-switched laser diode as ready-to-use qubits, the QKD transmitter can be radically simplified, eventually comprising a single laser and local phase tomography stage. We demonstrate our simplified transmitter by establishing a QKD link over a 10 km fiber, generating a secret key rate 110 bits/s, sufficient for practical deployment in "last mile" urban quantum networks. Our results show promise in making QKD simpler and more accessible, closing a critical technology gap in building a secure quantum communication infrastructure.